This invention relates to an improvement in a waste water treatment through an activated sludge process for purifying waste water, such as industrial waste water or living waste water by decomposing organic materials therein by using aerobic bacteria.
It is widely carried out to purify waste water containing organic materials through an activated sludge process. In the activated sludge process, organic materials in waste water are digested by microorganisms in an aeration tank, and then, the waste water is transferred to a sedimentation tank. Flocculated microorganisms, etc. are precipitated and separated there. The supernatant is, if necessary, further purified, and then discharged into river, etc. or utilized again.
Occasionally, centrifugation is substituted for the sedimentation tank.
A method of the purification is disclosed in Japanese Patent KOKAI 53-122249 which comprises adding a flocculant to the supernatant to flocculate residual microorganisms, etc., discharging carbon dioxide gas in the supernatant under conditions of pH 4.5 or lower, and then, adjusting the pH of the supernatant to neutral region where the librated ammonia concentration is 1.5 ppm or less.
Another method of the purification is disclosed in Japanese Patent KOKOKU 64-4837 which comprises of adding an inorganic flocculant and an organic polymer flocculant to the supernatant to form sludge flocs, and then, separating the precipitates of the sludge flocs to obtain purified waste water.
The inventors reported a waste water treatment in a glutamic acid manufacturing factory comprising of treating the waste water with an activated sludge process, adding a flocculant to the supernatant to flocculate residual organic materials, pigments, etc., separating the precipitated flocculates, and then, treating the supernatant with activated carbon (KOGAI TO TAISAKU, vol. 27, No. 8, pp 759-763, 1991). In the report, relations between the type of flocculant and pH, decoloration degree or precipitatability of flocculates were also reported.
Incidentally, the point of waste water treatment is in how to remove contaminates surely and efficiently by inexpensive means.
The method disclosed in Japanese Patent KOKAI 53-122249 purifies waste water sophisticatedly in view of resolving problems of discharged water treated with activated sludge process in living of fishes. This method utilizes a combination of an inorganic flocculant and a polymer flocculant, but does not disclose to add them in two steps with varying pH, etc.
The method disclosed in Japanese Patent KOKOKU 64-4837 improves the high load treatment of activated sludge and precipitation concentration of flocculated sludges from the supernatant. By increasing the concentration of suspended matters, the high load treatment is achieved, and by flocculating using an inorganic flocculant and an organic polymer flocculant, flocculation of flocs is improved. In this method, the inorganic flocculant and the organic polymer flocculant are successively added. However, pH is adjusted to 5, and this method does not disclose to treat in two steps with varying pH.